The present invention concerns a semiconductor device having a trench gate electrode.
High withstanding voltage semiconductor devices include semiconductor devices of a type having a trench gate electrode, for example, vertical MOSFET or IGBT. A requirement for such semiconductor devices is that on resistance should be low. Refinement of semiconductor devices is a method for lowering the on resistance. However, along with refinement, a problem has been caused in recent years in that the distance between gate electrodes is decreased to increase the parasitic capacitance of the gate electrode. In view of the above, FOM (Figure Of Merit), that is, (on resistance)×(parasitic capacitance of gate electrode) has been used recently as one of the measures showing the performance of a semiconductor device having the trench gate structure.
One of the techniques of improving FOM includes a method of lowering the on resistance by adopting a structure of ensuring the withstanding voltage of the semiconductor device to increase the impurity concentration of an epitaxial layer and lower the resistance. For example, P. Goarin, et al. disclose a method of ensuring the withstanding voltage of a semiconductor device by forming a deep trench and forming a thick oxide film inside the trench (Proceedings of 19th International Symposium on Power Semiconductor Devices & ICs, 2007, pp. 61-64). Further, Y. Kawashima, et. al disclose a method of ensuring the withstanding voltage of a semiconductor device by using a pn junction (Proceedings of the 22nd International Symposium on Power Semiconductor Devices & ICs, 2010, pp. 329-332). Japanese Unexamined Patent Publication No. 2009-32951 describes that the lowering of the withstanding voltage of the semiconductor device can be prevented by extending a well as far as a peripheral region adjacent to a cell region.
Japanese Unexamined Patent Publication No. 2001-217419 describes that local increase of an electric field intensity exerting on a gate insulating film can be prevented by forming corners of the trench substantially in an arcuate shape in a planar layout.